Active Suspension of a Motor Vehicle Passenger Seat

ABSTRACT

A method for controlling the operation of an active suspension system for a motor vehicle passenger seat, where the active suspension system comprises an actuator that is constructed and arranged to place force on the seat in a first degree of freedom and a control system that is responsive to a sensor system that detects motor vehicle accelerations in at least the first degree of freedom, where the sensor system comprises an accident detection system that detects motor vehicle accident conditions, where the control system provides control signals that cause the actuator to exert a force on the seat in the first degree of freedom, wherein in normal active suspension operation mode the actuator is controlled to output forces that reduce acceleration of the seat so as to counteract motions of the seat in the first degree of freedom. In response to the detection of an accident condition, the control system is used to operate the actuator in a crash performance mode where the actuator is controlled to output a force that is proportional to the velocity of the seat in the first degree of freedom.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Provisional Patent Application Ser.No. 61/830,936 filed on Jun. 4, 2013.

FIELD

This disclosure relates to the active suspension of a seat of a motorvehicle.

BACKGROUND

Active suspension can be used to counteract unwanted motions of the seatof a motor vehicle; most times the seat that is controlled is thedriver's seat but active suspension can be used for any passenger seat.Drivers can experience significant fatigue due to constant seatvibration. Other motions of the seat can also be uncomfortable, or evendangerous. Fatigue and seat-motion related issues can be lessened byusing active suspension to reduce seat vibration and other unwantedmotions of the seat.

SUMMARY

An active suspension system can be used to counteract unwanted motionsof a motor vehicle seat and an occupant sitting in the seat during anunusual event such as a collision or rollover. An active suspensionsystem uses one or more actuators that provide an output motion to helpaccomplish desired seat suspension and seat movement results. Examplesof such actuators include electromagnetic actuators, such as linearmotors and rotary motors that drive a transmission mechanism thatconverts rotary motion to linear motion, hydraulic actuators andpneumatic actuators. The subject active suspension system has anactuator that is constructed and arranged to place force on the seat ina first degree of freedom, and a sensor system that detects motorvehicle accelerations in at least the first degree of freedom. Anactuator control system that is responsive to the sensor system providescontrol signals that cause the actuator to exert a force on the seat inthe first degree of freedom so as to counteract unwanted motions of theseat. The sensor system is used to detect the motor vehicle experiencingconditions consistent with a vehicle having an accident, such asacceleration in a second degree of freedom that is different than thefirst degree of freedom. In response to this, the actuator controlsystem alters controller behavior and/or provides control signals thatcause the actuator to exert a force on the seat in the first degree offreedom.

All examples and features mentioned below can be combined in anytechnically possible way.

In one aspect, a method for controlling the operation of an activesuspension system for a motor vehicle passenger seat, where the activesuspension system comprises an actuator that is constructed and arrangedto place force on the seat in a first degree of freedom and a controlsystem that is responsive to a sensor system that detects motor vehicleaccelerations in at least the first degree of freedom, where the sensorsystem comprises an accident detection system that detects motor vehicleaccident conditions, where the control system provides control signalsthat cause the actuator to exert a force on the seat in the first degreeof freedom, wherein in normal active suspension operation mode theactuator is controlled to output forces that reduce acceleration of theseat so as to counteract motions of the seat in the first degree offreedom includes, in response to the detection of an accident condition,using the control system to operate the actuator in a crash performancemode where the actuator is controlled to output a force that isproportional to the velocity of the seat in the first degree of freedom.

Embodiments may include one of the following features, or anycombination thereof. An accident condition indicative of a front-endcollision may be detected based on the detection of a decelerationgreater than a predetermined threshold along the forward direction oftravel of the motor vehicle, and in response the actuator may becontrolled to exert an upward force on the seat. The actuator may beelectrically operated, and the control system may interrupt the power tothe actuator a predetermined time after the detection of an accidentcondition. The actuator may be an electromagnetic motor with power inputleads, and after the predetermined time the actuator may be operated inan unpowered failsafe mode where the leads are shorted.

Additional embodiments may include one of the following features, or anycombination thereof. The active suspension system may further comprise adamper with a variable damping coefficient, where the damper isconstructed and arranged to apply a variable resistive force thatopposes relative motion of the seating surface of the seat with respectto the seat base, wherein in the normal active suspension operation modethe damper is controlled to have a relatively low damping coefficient,and wherein in crash performance mode the damper is controlled to have agreater damping coefficient. In the crash performance mode the dampermay be controlled to have a greater damping coefficient only if adownward velocity of the seat exceeds a threshold velocity. The methodmay further comprise detecting, based on the sensor system, a rolloverof the motor vehicle and in response to the detection of a rolloverusing the control system to provide control signals that cause theactuator to exert a downward force on the seat. The actuator may be anelectromagnetic motor with power input leads, and the method may furthercomprise in response to the detection of a rollover using the controlsystem to interrupt the power to the actuator and short the leads apredetermined time after the detection of the rollover. The method mayfurther comprise detecting, based on the sensor system, an imminentaccident and in response to the detection of an imminent accident usingthe control system to provide control signals that cause the actuator toexert an upward force on the seat.

Additional embodiments may include one of the following features, or anycombination thereof. The seat may be located above the floor of themotor vehicle cabin and the actuator may be coupled to the seat, and theactive suspension system may further comprise a spring with a variablespring constant, where the spring is also coupled to the seat. Themethod may further comprise detecting, based on the sensor system, arollover of the motor vehicle and in response to the detection of arollover using the control system to provide control signals that causethe actuator to exert a downward force on the seat and cause the springconstant to quickly decrease, such control signals provided before theactuator is controlled to output a force that is proportional to thevelocity of the seat in the first degree of freedom. The spring maycomprise an expandable and contractible air container, and causing thespring constant to quickly decrease may comprise causing air to beexpelled from the air container. The active suspension system mayfurther comprise a damper with a variable damping coefficient, where thedamper is constructed and arranged to a apply a variable resistive forcethat opposes relative motion of the seating surface of the seat withrespect to the seat base, wherein in the normal active suspensionoperation mode the damper is controlled to have a relatively low dampingcoefficient, and the method may further comprise in response to thedetection of a rollover using the control system to cause the dampingcoefficient of the damper to remain relatively low. The seat may have alowest controlled position and in response to the detection of arollover, when the seat reaches its lowest controlled position thecontrol system may be used to increase the damping coefficient of thedamper.

Additional embodiments may include one of the following features, or anycombination thereof. The active suspension system may comprise at leastfirst and second actuators, where the first actuator is constructed andarranged to place force on the seat in a first degree of freedom of theseat and the second actuator is constructed and arranged to place forceon the seat in a second degree of freedom of the seat that is differentfrom the first degree of freedom, the method further comprising: inresponse to the detection of an accident condition, using the controlsystem to operate the actuators in a crash performance mode where thefirst actuator is controlled to output a force in the first degree offreedom and the second actuator is controlled to output a force in thesecond degree of freedom. The sensor system may comprise an inertialsensor that senses motions of the seat and a non-inertial sensor thatsenses motions of the seat, wherein in the normal active suspensionoperation mode the control system is responsive to both the inertial andnon-inertial sensors, and wherein in response to the detection of anaccident condition the control system becomes responsive only to thenon-inertial sensor, and is not responsive to the inertial sensor. Thesensor system may comprise at least one sensor that is part of the motorvehicle and is not part of the active suspension system, where thesensor is constructed and arranged to transmit sensor signals to thecontrol system, and wherein the control system is adapted to receive thesensor signals and in response generate control signals that cause theactuator to exert forces on the seat. In a truck with a cab thatincludes the passenger seat, and a separate trailer that is coupled tothe cab, the sensor system may comprise one or more sensors that detectone or more of: motion of the cab, motion of the trailer, relativemotion between the trailer and the cab, and relative forces between thetrailer and the cab. The method may further comprise detecting, based onthe one or more sensors that detect motion of the cab, or relativemotion or forces between the trailer and the cab, a rolling motion ofthe trailer that is greater than a threshold rolling motion, indicativeof a potential rollover of the motor vehicle.

In another aspect, a method for controlling the operation of an activesuspension system for a motor vehicle passenger seat, where the activesuspension system comprises: a first actuator that is constructed andarranged to place force on the seat in a first translational degree offreedom that is generally vertical with respect to the earth; a secondactuator that is constructed and arranged to place force on the seat ina second translational degree of freedom that is different than thefirst degree of freedom and is generally horizontal with respect to theearth and transverse to the forward direction of travel of the motorvehicle; and a control system that is responsive to a sensor system thatdetects motor vehicle accelerations in at least the first and seconddegrees of freedom and that comprises an accident detection system thatdetects motor vehicle accident conditions, where the control systemprovides control signals that cause the actuators to exert forces on theseat in the first and second degrees of freedom, wherein in normalactive suspension operation mode the first actuator is controlled tooutput forces that reduce accelerations of the seat, may include, inresponse to the accident detector detecting a rollover or impactaccident condition, using the actuator control system to operate theactuators in a crash performance mode where the first actuator iscontrolled to output a force in the first degree of freedom and thesecond actuator is controlled to output a force in the second degree offreedom and in a direction along the second degree of freedom that isaway from the side onto which the vehicle is rolling or the side thatwas impacted.

In another aspect, a method for controlling the operation of an activesuspension system for a motor vehicle passenger seat, where the activesuspension system comprises an actuator that is constructed and arrangedto place force on the seat in a first degree of freedom and a controlsystem that is responsive to a sensor system that detects motor vehicleaccelerations in at least the first degree of freedom and that comprisesan accident detection system that detects motor vehicle accidentconditions, where the sensor system comprises an inertial sensor thatsenses motions of the seat and a non-inertial sensor that senses motionsof the seat, and where the control system provides control signals thatcause the actuator to exert a force on the seat in the first degree offreedom, wherein in normal active suspension operation mode the actuatoris controlled to output forces that reduce accelerations of the seat,may include wherein in the normal active suspension operation mode thecontrol system is responsive to both the inertial and non-inertialsensors, and in response to the detection of an accident condition, thecontrol system becomes responsive only to the non-inertial sensor, andis not responsive to the inertial sensor.

In another aspect, a method for controlling the operation of an activesuspension system for a motor vehicle passenger seat, where the activesuspension system comprises an actuator that is constructed and arrangedto place force on the seat in a first degree of freedom and a controlsystem that is responsive to a sensor system that detects motor vehicleaccelerations in at least the first degree of freedom and that comprisesa system that detects one or more of a motor vehicle accident and animminent accident, wherein the sensor system comprises at least onesensor that is part of the active suspension system, where the sensor isconstructed and arranged to transmit sensor signals to the controlsystem, and where the control system provides control signals that causethe actuator to exert a force on the seat in the first degree offreedom, wherein in normal active suspension operation mode the actuatoris controlled to output forces that reduce accelerations of the seat,and where the motor vehicle has a vehicle data network thatcommunicatively interconnects the active suspension system with adifferent motor vehicle system, may include in response to the detectionof an accident or an imminent accident, using the control system tooperate the actuator to place force on the seat in the first degree offreedom and communicating over the network to the different motorvehicle system a signal that is related to the accident or imminentaccident.

In another aspect, a method for controlling the operation of an activesuspension system for a motor vehicle passenger seat, where the activesuspension system comprises an actuator that is constructed and arrangedto place force on the seat in a first degree of freedom, a damper with avariable damping coefficient, where the damper is constructed andarranged to a apply a variable resistive force that opposes relativemotion of the seating surface of the seat with respect to the seat base,and a spring with a variable spring constant, where the spring isconstructed and arranged to place force on the seat in the first degreeof freedom, and a control system that is responsive to a sensor systemthat detects motor vehicle accelerations in at least the first degree offreedom, where the sensor system comprises an accident detection systemthat detects motor vehicle accident conditions, where the control systemprovides control signals that cause the actuator to exert a force on theseat in the first degree of freedom, wherein in normal active suspensionoperation mode the actuator is controlled to output forces that reduceacceleration of the seat so as to counteract motions of the seat in thefirst degree of freedom, may include detecting, based on the sensorsystem, a rollover of the motor vehicle and in response to the detectionof a rollover using the control system to provide control signals thatcause the actuator to exert a maximum downward force on the seat, causethe spring constant of the spring to quickly decrease, and cause thedamping coefficient of the damper to be relatively low. In response tothe detection of a rollover, after the seat is pulled down by theactuator the control system may be used to operate the actuator tooutput a force that is proportional to the velocity of the seat in thefirst degree of freedom.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an active suspension system for a motorvehicle passenger seat.

FIG. 2 is a flow chart illustrating an operation of an active suspensionsystem for a motor vehicle passenger seat.

FIG. 3 illustrates an example of the vertical (z) position of a seatover time during a front-end collision.

FIG. 4 is a plot of the x-z position of the head of the occupant of aseat during a front-end collision.

FIG. 5 is a block diagram of an active suspension system for a motorvehicle passenger seat.

FIGS. 6A and 6B together are a flow chart illustrating an operation ofthe active suspension system for a motor vehicle passenger seat of FIG.5.

FIG. 7 is a flow chart illustrating an operation of the activesuspension system for a motor vehicle passenger seat of FIG. 5.

FIG. 8 is a block diagram of a motor vehicle network that includes theactive seat.

DETAILED DESCRIPTION

An active suspension system for a motor vehicle passenger seat (which issometimes termed herein an “active seat”) can be designed and operatedso as to inhibit downward motion of the seat during a front-endcollision. More generally, during an accident the actuator of the activesuspension system can be controlled to output a force that isproportional to the velocity of the seat. The active suspension systemcan also be designed and operated so as to quickly pull the seat downtoward the floor during a rollover; as the rollover proceeds that seatcan be moved in more than one degree of freedom in ways that counteractthe seat motions caused by the rollover. The active seat can communicatewith existing vehicle systems over the existing vehicle datacommunication network.

Embodiments of the systems and methods described here comprise computercomponents and computer-implemented steps that will be apparent to thoseskilled in the art. For example, it should be understood by one of skillin the art that the computer-implemented steps may be stored ascomputer-executable instructions on a computer-readable medium such as,for example, floppy disks, hard disks, optical disks, Flash ROMS,nonvolatile ROM, and RAM. Furthermore, it should be understood by one ofskill in the art that the computer-executable instructions may beexecuted on a variety of processors such as, for example,microprocessors, digital signal processors, gate arrays, etc. For easeof exposition, not every step or element of the systems and methodsdescribed above is described herein as part of a computer system, butthose skilled in the art will recognize that each step or element mayhave a corresponding computer system or software component. Suchcomputer system and/or software components are therefore enabled bydescribing their corresponding steps or elements (that is, theirfunctionality), and are within the scope of the disclosure.

Active suspension system 10, FIG. 1, uses actuator 14 to place forces onmotor vehicle seat 12. Actuator 14 is coupled (either directly orindirectly) to both seat 12 and another portion of the motor vehicle,which in this non-limiting example is the cabin floor 20. Actuator 14 inthis example applies forces linearly along first degree of freedom “A,”which here is vertically up and down. This can move (translate) the seatup and down. Actuator 14 may be an electromagnetic actuator, for examplea linear motor or a rotary actuator with a rotary to linear motiontransmission, as is known in the art. Actuator 14 can alternatively behydraulically or pneumatically actuated.

System 10 in its typical operation uses sensor system 16 to senseaccelerations of a location of the motor vehicle in this same firstdegree of freedom; this location is commonly the seat, the vehicle frameor the vehicle body. Control system 18 interprets the sensedaccelerations and initiates control signals that are provided toactuator 14 to counteract seat motion caused by the sensedaccelerations. One example of accelerations is vibrations and joltscaused by operation and motion of the motor vehicle while driving alonga road. The result of such active seat suspension is to reduceaccelerations of the seat, which will decrease vertical motions of theseat caused by such vibrations and jolts.

Sensor system 16 can also sense a quantity related to motion such asaccelerations (or other quantities representative of vehicle motion suchas velocity in any direction, roll angle, roll rate, pitch angle, pitchrate, etc.) of the motor vehicle in second degree of freedom “B,” whichis different that the first degree of freedom. In one example thissecond degree of freedom is horizontal translation, e.g., accelerationsand decelerations in the direction of travel of the motor vehicle.However, this second degree of freedom could be any one or more of theother of the remaining five of the six degrees of freedom of the motorvehicle. In response to motions or accelerations sensed in degree offreedom B, control system 18 alters controller behavior as will bedescribed later, and/or provides control signals to actuator 14 to causethe actuator to exert forces on seat 12 in first degree of freedom A.Typically these forces are meant to accomplish a particular desiredresultant motion of the seat and/or the occupant of the seat.

An accident detection system may detect accident conditions by sensingaccelerations and/or other motions such as rotations and/or angle, inone or more degrees of freedom, as accomplished by sensor system 16described above. Alternatively, an accident detection system candetermine if accident conditions are present or are imminent using othermeans. In one example, an accident detection system uses optical,electromagnetic (i.e. radar), or other sensing means to determine if thevehicle in which the active seat resides is about to collide withanother vehicle. The controller can change its behavior and/or thecontroller can issue control commands to the actuator to output a forcein response to the determination that an accident condition is eitherprobable or imminent. The accident detection system may be incorporatedas part of the active seat system, or it may be incorporated in someother part of the vehicle. In the case where the accident detectionsystem is not incorporated in the active seat, the accident detectionsystem is in communication with the active seat and informs the activeseat controller when an accident is either probable or imminent, or whenan accident is occurring.

One use of system 10 is to counteract the effects of an event that canlead to possible injury of an occupant of the vehicle, such as a head-oncollision, a partial front-end collision, a side collision, a direct orpartial rear-end collision, or a rollover. For example, a collision canbe determined based on sensor system 16 detecting the axis (or axes) andmagnitudes of accelerations in one or more of the six degrees of freedomof the motor vehicle. Flow chart 30, FIG. 2, illustrates one of manypossible manners in which system 10 can be operated in forward impact(i.e., front end collision) and rollover situations. Sensor system 16 iscontinually monitored for unusual accelerations (events) in one or moredegrees of freedom, step 32. If no event is detected normal operation ofthe active suspension termed “normal active suspension mode”, where thesuspension is used to counteract vibrations arising from normaloperation of the vehicle, is maintained, step 33. For example, in normaloperation, the controller implements a negative feedback loop aroundacceleration of the seat top in order to minimize acceleration of theseat top.

As a non-limiting example of the detection of an event, an accelerationin any degree of freedom that is greater than a predetermined maximumnormal acceleration can be determined to be an “event”, step 32. As mostvehicles will not normally experience an acceleration approaching 30m/s/s (3 g), the event threshold can be set to 3 g (although otherthresholds could be set if desired). At step 34 the event ischaracterized based on the sensed accelerations and their degrees offreedom. For example, a forward impact could be determined if a forwarddeceleration of at least 3 g is sensed, step 35, and a rollover can bedetermined if the vehicle has rolled more than, say, 45° (i.e., thedetected roll angle is greater than 45°), step 38. If a forward impactis detected, “crash performance mode” is entered, step 36, and thecontroller behavior is altered and/or the actuator is commanded tooutput a force, step 37. For example, the controller may switch behaviorfrom implementing a negative feedback loop around acceleration of theseat to implementing a negative feedback loop around relative velocityof the seat top with respect to the vehicle floor. If the seat begins tomove down in a forward impact, the result can be that the actuator iscommanded to push the seat up. If a rollover is detected “crashperformance mode” is entered, step 39, and the actuator is commanded tooutput a force to pull the seat down, step 40. The “crash performancemode” can be set to expire a pre-determined time after the event wasdetected; in one case the time is 200 milliseconds (mS) and isdetermined at step 41. After this time the system enters the actuatorpassive mode, step 42, where current to the actuator is limited to asmaller value than normal operating mode or to zero, thus de-energizingthe motor. Additionally, in actuator passive mode the actuator coilpower input leads may be clamped to short circuit the coils, causing theactuator to act like a passive mechanical damper. Some of these actionsare further described below.

Some motor vehicle seat active suspension systems, such as the Ridesystem available from Bose Corporation of Framingham, Mass. USA, use afour-bar seat suspension base linkage between the floor of the cabin andthe seat support that supports the seat on which the passenger sits. Thelinkage supports the seat and allows it to be moved vertically by theactuator(s). When a vehicle with this system experiences a front-endcollision and the person in the seat is constrained by a seatbelt whichis anchored to the Bose Ride interconnection point (ICP) and to thefloor just behind the seat, the momentum of the seat and the personcauses the person's upper body to pivot forward and down about the hips.This causes the linkage to compress and thus causes the seat to movedown. One result is that the occupant's head moves forward and down,thus moving the head closer to the steering wheel, the dash anddeploying vehicle airbags. Such excursions of the head beyond its normalposition may lead to serious head trauma.

In an exemplary active suspension system 10, actuator 14 comprises alinear motor with a maximum output force of 1000 Newtons (N). In a frontend collision where the seat and the occupant have a mass of 100 Kg andthe maximum deceleration is 22 g, the horizontal motion couples througha 7.5 degree four-bar link to yield approximately 3000N of downwardforce. This can cause a downward seat velocity of about 2 meters persecond (m/S). The actuator 14 may have a vertical full stroke of about100 mm, around nominal mid-height adjustment before it physicallybottoms out. Since the seat is coupled to the actuator, during afront-end collision the front of the seat may collapse 50 mm, if theactuator was at nominal mid-height adjustment pre-crash.

In “normal active suspension operation mode”, the Bose Ride system has afailsafe operating mode where the active system is switched intooperation in the passive actuator mode whenever a fault is detected. Oneexample of a fault condition would be saturation or failure of a sensor,which could happen for a number of reasons. In failsafe operating mode,the system remains in passive mode until the fault is corrected. Oncethe fault is no longer present, the system reverts back to normal activesuspension operation mode. When an accident occurs, it is highly likelythat the system accelerometers will saturate or have erroneous output.The output signals from inertial measurement devices such asaccelerometers cannot be trusted when high acceleration or highdeceleration events such as a crash event occur. If the system were toswitch into failsafe operation, the actuator would operate in itspassive, clamped state as a mechanical damper. In this state, themaximum damping force provided by the actuator will be less than theavailable maximum force if the actuator were operated in an activestate. In passive clamped state, the damping coefficient of the actuatoris fixed by the actuator design.

In the event of a crash, an actuator operated in a passive state is lessable to resist the crash forces than if it were allowed to operate in anactive state. If the actuator were allowed to remain active when a crashis detected, it could, for example, be controlled to operate as aphysical damper where the damping coefficient could be set arbitrarily,and could be as high as is physically possible given the maximum outputforce capability of the actuator. In one non limiting example, in acrash the controller behavior is altered such that it implements anegative feedback loop around the relative velocity of the seat top withrespect to the vehicle floor. In this mode, the controller makes thesystem look like a physical damper where the damping coefficient iscontrolled in order to minimize the relative velocity of the seat toprelative to the vehicle floor.

The motor can be operated to slow the seat downward motion by allowingthe active suspension system to remain active such that the motor canoutput up to its full 1000N of force upon the detection of an event orcrash such as a forward impact. The graph of FIG. 3 illustrates thisbenefit. Vertical seat movement (z position) is plotted on the y axiswith time in milliseconds (mS) on the x axis. Nominal operationalvertical seat position is at 0 mm in the z position. The event begins at0 mS. The event is detected by the control system at 20 mS. At about 60mS the seat begins to move downward at high velocity. If the system wereto operate in the failsafe mode with the actuator leads clamped, themotor force output would be restricted to what can be generated by themotor back EMF which has a maximum force of approximately 400N. In thiscondition, the seat motion would follow plot 43 (solid line) and wouldbottom out (−50 mm z position) at about 85-90 mS. When the motor iscontrolled to have full force output of 1000N available, for examplewhen in “crash performance mode” where the controller implements anegative feedback loop around the relative velocity of the seat top withrespect to the vehicle floor, the seat motion will follow plot 44(dashed line) and bottom out at about 125 mS. Also, note that at 100 mSthere is significantly less vertical displacement (50 mm versus 22 mm,thus a reduction of about 28 mm).

The graph of FIG. 4 illustrates the occupant's head movement in thevertical (z) and horizontal (x) directions through time during thepreviously described front end collision. The motion that moves from thepre-crash position 45, through points 46 a, 47 a and ending at 48 a(plotted as a solid line) is based on the system 10 while operating in“normal active suspension operation mode”, where upon detection of afault condition (such as accelerometer saturation as may occur in acrash, or upon detection of a crash event by a crash event detectionsystem), the actuator is operated in passive, clamped mode. The maximumforward (x) excursion of the forehead is noted by the right-most point46 a, which is forward about 560 mm from the pre-crash position 45 andoccurs at about 80-90 mS post-crash. The maximum vertical (z) excursionof the head is about −350 mm (downward) at point 47 a from the pre-crashposition 45 and occurs at about 120 mS post-crash. Since the maximumforward excursion of the head occurs in under 100 mS, it would bebeneficial to slow the time when the seat bottoms out until after 100 mSpost-crash. One result would be that the seat would bottom out after thehead had begun to retract away from its forward-most point, toward endpoint 48 a.

The motion that moves from the pre-crash position 45, through points 46b, 47 b and ending at 48 b (plotted as a dashed line) is based on thesystem 10 while operating in “ ” crash performance mode”, where thecontroller has been altered to implement a negative feedback loop aroundthe relative velocity of the seat top with respect to the vehicle floor,and the actuator has remained active. The maximum forward (x) excursionof the forehead is noted by the right-most point 46 b, which is lessthan point 46 a. The maximum vertical (z) excursion of the head is notedby 47 b which is less than 47 a. The ending point 48 b exhibits lessvertical displacement and horizontal displacement as compared to 48 a.One result of this difference in motion is that the chances of impactwith the dash or with a deploying airbag are reduced.

One example of an active suspension system 50 for a motor vehiclepassenger seat 52 is shown in FIG. 5. System 50 includes seatpositioning system 51 which has two separate actuators and a variabledamping coefficient damper such as a variable force shock absorber.Variable spring 54 has a variable spring constant. In one non-limitingexample spring 54 is an air cylinder or another type of pneumatic orhydraulic system with variable force output, and is commonly used as aforce bias eliminator. Spring 54 acts as a load-leveling system whosegoal is to reduce the average force that the actuator (linear motor)needs to output to control motion of the seat in the intended degree offreedom during normal operation to zero. Control to reduce the averageforce to zero involves both adding air and removing air from the aircylinder. As explained below, pneumatic cylinder 54 can include anelectrically-operated valve 55 that can be opened to quickly expel airfrom the cylinder in a crash event. The second actuator is linear motor56, which acts to place vertical forces on seat 52 to push or pull theseat in opposition to sensed vertical accelerations. Shock absorber 58is a damper with a variable damping coefficient. Shock absorber 58 ismounted in parallel with the actuators and is used to apply additionaldamping or resistive force on the seat as needed to damp seat motion, asfurther explained below.

An active suspension system can be designed to counteract and/or dampmotions in any one or more of the six degrees of freedom of the vehicleseat. There is typically at least one active actuator or a passivesuspension for each degree of freedom of concern. For example, a systemcan actively control in the vertical axis and have passive suspensionsystems in the X and Y axes of the horizontal plane of the seat. Or, thesystem may have active control in the vertical (z) axis and thehorizontal (y) lateral axis which is perpendicular to the direction oftravel (x axis) of the motor vehicle. Typical passive suspensions arecombinations of springs and dampers. Resonant absorbers can also adddamping masses.

When a vehicle is involved in a front-end collision there is a suddenhorizontal deceleration. As described above, in an active seat systemwith at least vertical axis active control such as shown in FIG. 5 thedeceleration causes forward/downward pivoting motion of the torso andhead that can be exacerbated by the reaction of spring 54. Since spring54 is relatively soft in comparison to the downward forces on the seatin a front-end collision, the spring can compress. Due to the forwarddynamics of a front-end collision, the mechanical structure under theseat top will tend to tilt forward. The seatbelt tethers connectedbetween the ICP and the floor prevents the rear of the seat system frommoving beyond a certain point. The front of the seat system is notlimited by any means vertically and will dip down. The result is thatthe seat top and occupant will be thrown forward and downward. Theresult can be an extreme forward excursion of the head.

System 50 can be arranged to counteract these excursions by using linearmotor 56 to exert an upward force on seat 52 upon the detection of afront-end collision. This force can help to maintain seat 52 closer toits pre-crash vertical position than would be the case without theapplication of such upward force. This force can also help to maintainseat 52 in a more horizontal position; i.e., it can inhibit or at leastslow the pivoting of the seat relative to the cabin floor. Either orboth of these results of upward vertical force on the seat will help todecrease the forward motion of the torso and head, which can ameliorateinjuries caused by the collision.

Active suspension system 50 includes inertial measurement system 60 thatis coupled to seat 52 so as to sense accelerations and/or rotations ofthe seat along and/or about one, two or three orthogonal axes in space.Thus system 60 acts as inertial sensor in from one to six degrees offreedom of the seat. Its output is provided to control system 64. Seatposition sensor 61 is not an inertial measurement instrument. Seatposition sensor 61 may employ magnetic sensors on the stator andarmature of a linear motor actuator as described in U.S. Pat. No.7,932,684 which is incorporated herein by reference. Since sensor 61 isnot inertial it does not become unreliable in a crash as inertialsensors might. In crash performance mode the controller thus may relysolely on sensor 61 and ignore sensor system 60. Control system 64interprets the outputs from one or both of inertial measurement system60 and seat position sensor 61 and creates control signals that causelinear motor 56 and/or spring 54 and/or shock absorber 58 to actaccordingly. These actions can include placing force(s) and/or dampingmotions on the seat in any one or more of its six degrees of freedom(presuming that the appropriate actuators and dampers are in place so asto accomplish the forces and damping). One aim of such actions can be toposition the occupant in the case of an unusual event such as an impactor rollover, so that impacts of the occupant with the motor vehicleinterior are less likely to occur, or their severity is lessened.

One example of operation of system 50 in the case of a front-endcollision is illustrated by flowchart 130, FIGS. 6A and 6B. Upon thedetection of a lateral or fore/aft acceleration greater than 3 g (e.g.,forward impact 132) the system first enters a “crash performance mode”,step 134. While in this mode, the system may command an amount ofactuator force that is related to (e.g., proportional to) the downwardvelocity of the seat and that can be greater than the amount of actuatorforce that is normally available in the failsafe operation associatedwith the “normal operating mode,” up to the maximum actuator force. Thefaster that the seat moves downward, the greater the upward forceprovided by the actuator. The goal is to maintain the pre-crash verticalseat position. In one example, the control system can be operated suchthat the actuator force is equal to the seat velocity multiplied by anegative constant. This causes the actuator to act as a linear shockabsorber that damps downward motion of the seat. In another example thecontroller implements a negative feedback loop around relative velocityof the seat top with respect to the vehicle floor. In this case, thesystems acts like a mechanical damper with a damping coefficient that isvaried as needed to minimize the relative velocity. In another examplethe controller could implement a negative feedback position loop to tryto maintain seat top position relative to the vehicle floor. In anotherexample an acceleration signal could be derived from the seat positionsensor, in which case operation can continue with an accelerationcontrol loop as described above. In one example, a three-axisaccelerometer is mounted to this seat structure and is monitored morethan 2000 times per second. From the measured acceleration, velocity anddistance can be derived mathematically by the system, step 136.Alternatively, since inertial measurement instruments such asaccelerometers can become unstable and unreliable in high-g events suchas front-end collisions, the seat velocity can be determined based onthe derivative of the output of non-inertial seat position sensor 61.Once the seat velocity has been determined the system can apply anappropriate current to the motor to establish the desired force.

An airbag can have more air pushed into it by opening the solenoids onthe air input lines. Truck air is typically 100 pounds per square inch(psi). Pneumatic control systems have slow reactance speeds. If theairbag valves were opened to add air during a crash event, this wouldnot create enough extra force to withstand the downward force due to theevent. Thus, spring 54 is not effective to maintain the verticalposition of the seat in a crash.

The vertical seat position can be improved by the creation of moresignificant opposing resistive forces, which would help to prevent thecollapsing of the seating system. A mechanical shock absorber with avariable damping coefficient mounted in parallel with the linear motorand the spring can be used to supply the needed additional verticalresistive force. This shock can be designed to not offer any substantialdamping (i.e., the damping coefficient is low) during normal operation(which can in one non-limiting example be defined by a vertical seatvelocity of no more than about 0.5 m/S). However, while the system is inthe crash performance mode and the seat velocity is greater than 0.5 m/Sindicative of an abnormal event such as a crash, step 138, the shock'sresistive force would be increased (i.e., its damping coefficient wouldbe increased). If while in the crash performance mode the seat velocityis less than 0.5 m/S, the system uses only the active linear motor tooppose downward seat motion; the necessary force is calculated at step140.

A magneto-rheological (MR) shock is one means of accomplishing thedesired force/velocity relationship to damp downward forces of more thanabout 1000N. As one non-limiting example the damping coefficient of theshock is controlled in normal operation to result in forces in the rangeof 0 to about 1000N. If a forward impact is detected, step 132, crashperformance mode is entered, step 134. If the measured downward seatvelocity is greater than 0.5 m/S, step 138, the controller operation ischanged, for example to implement a negative feedback loop around therelative velocity of the seat top with respect to the vehicle floorwhere maximum output force of the actuator remains available, step 142,and the additional resistive force that can be supplied by the linearmotor and that is needed to counteract the downward force (to be appliedby variable force shock 58) is calculated, step 144. The control systemcan calculate how much current to apply to the MR shock to obtain adesired output force. For example, if the system was moving downward at2 m/S, to obtain 2000N of force from the shock, about 2 A of currentwould be necessary. The seat velocity can be determined based on thederivative of the output signal of seat position sensor 61. In onemanner of operation of the control system, a control loop on velocitymay directly adjust the damping coefficient of shock 58.

The “crash performance mode” can be set to expire a pre-determined timeafter the accident or event (in this case, a front end collision) wasdetected; in this case the time is 200 mS and is determined at step 146.After this time the variable force shock is released (i.e., its dampingcoefficient is set to zero), step 148, and the system then enters thelinear motor passive mode, step 150, where current to the motor islimited to a smaller value than normal operating mode or to zero, thusde-energizing the motor, and the motor is clamped. Where the velocity isless than 0.5 m/S and the shock absorber was never engaged, step 148 isbypassed, in which case after 200 mS (step 146) the linear motor iscommanded to enter the passive mode, step 150.

Flowchart 160, FIG. 7, details an example of the operation of system 50upon detection of a rollover event, step 162. The system enters crashperformance mode, step 164. One goal of system 50 during a rollover isto pull the seat down as quickly as possible to help prevent theoccupant from impacting the ceiling of the cabin as the vehicle rollsonto or toward its roof. As variable force spring 54 is holding the seatup, it will inhibit downward movement of the seat. To facilitate theability of the seat to be moved downward, it is best to quickly decreasethe spring constant of the spring, which in this case is done byreleasing air from the air cylinder. This is done at step 166 by usingcontrol system 64 to open valve 55, which is designed to allow air to beexpelled quickly. Then at step 168 the linear motor is commanded toapply maximum downward force. After 5000 mS post-event, step 170, themotor is commanded to enter its passive, clamped mode, step 172. Onereason that the linear motor is applied for 5000 mS in a rollover andonly 200 mS in a front-end collision is that a rollover tends to occurover a longer period of time than a collision.

A front impact is sensed by reading the acceleration reported for the“X” axis. A movement in the X direction would give a +/− reading up tothe scale of the device. In a high-g crash scenario, an inertialmeasurement device such as an accelerometer will often saturate and besubject to severe cross-axis coupling that makes it an unreliablecontrol system input sensor. However, an accelerometer can act as anaccident or crash sensor. For example, with a device that saturates at 3g, a maximum output (e.g., 3 g) indicates an accident. Multiple samplescan be taken to determine this is not an instantaneous loss of signal.Sampling of the accelerometer at 2000 times/sec, means that for a crashpulse of 100 mS, there would be 200 samples. In practicality, 10consecutive samples would be enough to determine an accident or crashevent with some amount of confidence.

Methods to detect roll are well known in the art. In one non-limitingexample a three axis X/Y/Z accelerometer mounted to the upper mechanicalstructure of the seat suspension base can be used as inertialmeasurement system 60. To this structure the seat top is mounted. Theoccupant sits on the seat top. The accelerometer is mounted rigidly anddirectly below the center point of where the occupant sits. The X/Y/Zaccelerometer provides a digital value output that is scaled to theacceleration seen by each axis. Math can be used to determine the angleof rotation of the device relative to the “g” seen on each axis. Analternative means of measuring rotation would be to use a gyroscopedevice (e.g., a MEMS gyro) that can output angle. A typical MEMSaccelerometer is the KXRB5-2367, manufactured by Kionix, Inc. A typicalMEMS combined gyroscope and accelerometer is the MPU-6500, manufacturedby InvenSense, Inc.

A rollover can be sensed by deducing using calculations the angle ofrotation as reported by the X/Y/Z accelerometer, or by other methodsknown in the art. For example, if the accelerometer was rotated in oneaxis, a reading of less than 1 g would be measurable. Math can be usedto map the acceleration in an axis to an angle of rotation. A MEMSgyroscope can provide both a 3 axis gyroscope and 3 axis accelerometer.The determination that a forward impact has occurred can be based onwhen acceleration of more than 3 g is sustained for a period of samples.The determination that a rollover has occurred can be when a certainangle has been exceeded from an upright vertical position reading, e.g.,45 degrees.

Motor vehicle network 200, FIG. 8, comprises active seat 202 that is indata communication with existing motor vehicle systems such as collisionavoidance system 204, airbag deployment system 206, black box 208,information center 210, hazard lights 212 and collision detection system216. One or more of such systems communicates with one or more othersuch systems over existing vehicle data network 214, which typicallyuses an existing networking convention such as the controller areanetwork (CAN) vehicle bus standard or the local interconnect network(LIN), general purpose input/outputs (GPIO) or other existing motorvehicle communication standards as are known in the art.

In one exemplary use of network 200, in response to detecting animminent frontal impact crash, the collision avoidance system 204communicates such a status to the active seat system 202 via vehiclenetwork 214. In response to the received status, the active seat systemcould move the seat up from the pre-status vertical position so as toprovide greater range of controlled downward motion after the crashbefore the seat may reach the bottom limit of vertical mechanicaltravel. Another benefit of moving the seat up before an imminent frontalimpact crash is that there is less seat belt restraint system webbingout of the spool and that reduces the amount of webbing stretch thatcontributes to frontal excursion of the occupant towards the steeringwheel.

In a frontal impact crash, once the active seat motor is controlled toreach the optimal vertical position (e.g., all the way up), a MR dampercould be turned on to further resist any downward motion, as describedabove.

In one example, in response to detecting an imminent roll-over crash,the collision avoidance system 204 communicates such a status to theactive seat system 202 via vehicle network 214. In response to thereceived status, the active seat is proactively pulled down, asdescribed above. In response to determination that a crash condition isimminent but has not yet occurred, normal function of the seat isdiscontinued and the seat is moved to a position better suited toprotection of the seat occupant: in case of a frontal impact, the seatis moved upwards prior to the crash while in case of a rollover, theseat is moved down. In case of a side impact, the seat is moved awayfrom the side about to be impacted.

In a roll-over crash, an MR damper could be controlled off initially, orset to a minimum damping state, while the active seat motor is pullingthe seat down to the bottom limit of vertical mechanical travel. Oncethat limit has been reached, the MR damper could then be turned on(e.g., with maximum damping coefficient), so as to resist any upwardsvertical travel that could be caused by the occupant's weight.

In a roll-over crash or side collision crash and with an active seathaving two degrees of translational freedom, for example vertical andhorizontal lateral (i.e., z and y axes), it is advantageous to move theseat occupant away from the side of collision. For example, in roll-overcrash the active seat would be pulled down and also pushed away fromside of vehicle that is moving toward the earth. In a side collisioncrash, the active seat would be held in the vertical position while alsousing the lateral horizontal active isolation to move the occupant awayfrom the side of collision. In a frontal collision, the horizontalactive y-axis isolation would be locked/clamped/force applied to attemptto maintain a fixed nominal central position.

In one example, where the collision detection system 216 or an inertialsensor or another motion and/or force sensor is mounted in the trailerand/or in the trailer/cab coupling of a tractor trailer that has aseparate cab, it is possible that an imminent tipping of the trailercould be detected based on a rolling motion greater than a thresholdrolling motion. The sensor(s) would be in communication with the activeseat controller. The detection could take place prior to the roll-overof the cab that the occupant is in. In such a case, proactivepositioning of the occupant can be achieved using the active seat tomove the occupant towards an optimal position away from the roll-overside and pulling the seat downwards. Also, the imminent rollover couldbe reported and could potentially be counteracted.

In one example, where the collision includes a multitude of impactsand/or rolls, the active seat system 202 may sense and then communicatesuch information to an airbag deployment system 206 so as to sequencethe deployments of airbags surrounding the occupant in a manner thatprovides maximum protection to the side of impact. For example, when atruck rolls to the left, then onto the roof, then again to the left (andso onto the right side), the airbag deployed sequence may be to deployleft-side airbag, then right-side airbag. The deployment can be timedrelative to the rolling so that the airbag inflation occurs when theoccupant is being thrown to the side where the airbag is being inflated.This can be done in addition to actuated seat motions as describedabove.

In one example, the active seat system 202 may indicate the detection ofa collision to a hazard light controller 212 so that hazard lights canbe turned on.

In one example, the active seat system 202 may indicate the detection ofa collision to a black box 208 for logging of data, as a failsafetrigger to the self-monitoring by the black box and to provide dataregarding the seat movement of the occupant.

In one example, the active seat system 202 may indicate the detection ofa collision to an information center 210 that can communicate withemergency services or dispatcher so that status of the occupant can berelayed. Information, such as acceleration, derived by the active seatsystem could also be sent that can be used to understand the severity ofthe collision and hence ensure appropriate response is provided byemergency services.

A number of implementations have been described. Nevertheless, it willbe understood that additional modifications may be made withoutdeparting from the scope of the inventive concepts described herein,and, accordingly, other embodiments are within the scope of thefollowing claims.

1. A method for controlling the operation of an active suspension systemfor a motor vehicle passenger seat, where the active suspension systemcomprises an actuator that is constructed and arranged to be powered soas to place force on the seat in a first degree of freedom and a controlsystem that is responsive to a sensor system that detects motor vehicleaccelerations in at least the first degree of freedom, where the sensorsystem comprises an accident detection system that detects motor vehicleaccident conditions, where the control system provides control signalsthat cause the actuator to exert a force on the seat in the first degreeof freedom, wherein in normal active suspension operation mode theactuator is controlled to output forces that reduce acceleration of theseat so as to counteract motions of the seat in the first degree offreedom, the method comprising: in response to the detection of anaccident condition, using the control system to operate the actuator ina crash performance mode where the power to the actuator is controlledsuch that the actuator outputs a force that is proportional to thevelocity of the seat in the first degree of freedom.
 2. The method ofclaim 1 wherein an accident condition indicative of a front-endcollision is detected based on the detection of a deceleration greaterthan a predetermined threshold along the forward direction of travel ofthe motor vehicle, and wherein in response the actuator is controlled toexert an upward force on the seat.
 3. The method of claim 1 wherein theactuator is electrically operated and the control system interrupts thepower to the actuator a predetermined time after the detection of anaccident condition.
 4. The method of claim 3 wherein the actuatorcomprises an electromagnetic motor with power input leads, and whereinafter the predetermined time the actuator is operated in an unpoweredfailsafe mode where the leads are shorted.
 5. The method of claim 1wherein the active suspension system further comprises a damper with avariable damping coefficient, where the damper is constructed andarranged to apply a variable resistive force that opposes relativemotion of the seating surface of the seat with respect to the seat base,wherein in the normal active suspension operation mode the damper iscontrolled to have a relatively low damping coefficient, and wherein incrash performance mode the damper is controlled to have a greaterdamping coefficient.
 6. The method of claim 5 wherein in the crashperformance mode the damper is controlled to have a greater dampingcoefficient only if a downward velocity of the seat exceeds a thresholdvelocity.
 7. The method of claim 1 further comprising detecting, basedon the sensor system, a rollover of the motor vehicle and in response tothe detection of a rollover using the control system to provide controlsignals that cause the actuator to exert a downward force on the seat.8. The method of claim 7 wherein the actuator comprises anelectromagnetic motor with power input leads and the method furthercomprises in response to the detection of a rollover using the controlsystem to interrupt the power to the actuator and short the leads apredetermined time after the detection of the rollover.
 9. The method ofclaim 1 further comprising detecting, based on the sensor system, animminent accident and in response to the detection of an imminentaccident using the control system to provide control signals that causethe actuator to exert an upward force on the seat.
 10. The method ofclaim 1 wherein the seat is located above the floor of the motor vehiclecabin and the actuator is coupled to the seat, and wherein the activesuspension system further comprises a spring with a variable springconstant, where the spring is also coupled to the seat.
 11. The methodof claim 10 further comprising detecting, based on the sensor system, arollover of the motor vehicle and in response to the detection of arollover using the control system to provide control signals that causethe actuator to exert a downward force on the seat and cause the springconstant to quickly decrease, such control signals provided before theactuator is controlled to output a force that is proportional to thevelocity of the seat in the first degree of freedom.
 12. The method ofclaim 11 wherein the spring comprises an expandable and contractible aircontainer, and causing the spring constant to quickly decrease comprisescausing air to be expelled from the air container.
 13. The method ofclaim 11 wherein the active suspension system further comprises a damperwith a variable damping coefficient, where the damper is constructed andarranged to a apply a variable resistive force that opposes relativemotion of the seating surface of the seat with respect to the seat base,wherein in the normal active suspension operation mode the damper iscontrolled to have a relatively low damping coefficient, the methodfurther comprising in response to the detection of a rollover using thecontrol system to cause the damping coefficient of the damper to remainrelatively low.
 14. The method of claim 13 where the seat has a lowestcontrolled position and further comprising, in response to the detectionof a rollover, when the seat reaches its lowest controlled positionusing the control system to increase the damping coefficient of thedamper.
 15. The method of claim 1 wherein the active suspension systemcomprises at least first and second actuators, where the first actuatoris constructed and arranged to be powered so as to place force on theseat in a first degree of freedom of the seat and the second actuator isconstructed and arranged to be powered so as to place force on the seatin a second degree of freedom of the seat that is different from thefirst degree of freedom, the method further comprising: in response tothe detection of an accident condition, using the control system tooperate the actuators in a crash performance mode where the power to thefirst actuator is controlled such that the first actuator outputs aforce in the first degree of freedom and the power to the secondactuator is controlled such that the second actuator outputs a force inthe second degree of freedom.
 16. The method of claim 1 where the sensorsystem comprises an inertial sensor that senses motions of the seat anda non-inertial sensor that senses motions of the seat, wherein in thenormal active suspension operation mode the control system is responsiveto both the inertial and non-inertial sensors, and wherein in responseto the detection of an accident condition the control system becomesresponsive only to the non-inertial sensor, and is not responsive to theinertial sensor.
 17. The method of claim 1 wherein the sensor systemcomprises at least one sensor that is part of the motor vehicle and isnot part of the active suspension system, where the sensor isconstructed and arranged to transmit sensor signals to the controlsystem, and wherein the control system is adapted to receive the sensorsignals and in response generate control signals that cause the actuatorto exert forces on the seat.
 18. The method of claim 1 where the motorvehicle is a truck, where the truck has a cab that includes thepassenger seat, and the truck has a separate trailer that is coupled tothe cab, and where the sensor system comprises one or more sensors thatdetect one or more of: motion of the cab, motion of the trailer,relative motion between the trailer and the cab, and relative forcesbetween the trailer and the cab.
 19. The method of claim 18 furthercomprising detecting, based on the one or more sensors that detectmotion of the cab, or relative motion or forces between the trailer andthe cab, a rolling motion of the trailer that is greater than athreshold rolling motion, indicative of a potential rollover of themotor vehicle.
 20. A method for controlling the operation of an activesuspension system for a motor vehicle passenger seat, where the activesuspension system comprises: a first actuator that is constructed andarranged to place force on the seat in a first translational degree offreedom that is generally vertical with respect to the earth; a secondactuator that is constructed and arranged to place force on the seat ina second translational degree of freedom that is different than thefirst degree of freedom and is generally horizontal with respect to theearth and transverse to the forward direction of travel of the motorvehicle; and a control system that is responsive to a sensor system thatdetects motor vehicle accelerations in at least the first and seconddegrees of freedom and that comprises an accident detection system thatdetects motor vehicle accident conditions, where the control systemprovides control signals that cause the actuators to exert forces on theseat in the first and second degrees of freedom, wherein in normalactive suspension operation mode the first actuator is controlled tooutput forces that reduce accelerations of the seat, the methodcomprising: in response to the accident detector detecting a rollover orimpact accident condition, using the actuator control system to operatethe actuators in a crash performance mode where the first actuator iscontrolled to output a force in the first degree of freedom and thesecond actuator is controlled to output a force in the second degree offreedom and in a direction along the second degree of freedom that isaway from the side onto which the vehicle is rolling or the side thatwas impacted.
 21. A method for controlling the operation of an activesuspension system for a motor vehicle passenger seat, where the activesuspension system comprises an actuator that is constructed and arrangedto place force on the seat in a first degree of freedom and a controlsystem that is responsive to a sensor system that detects motor vehicleaccelerations in at least the first degree of freedom and that comprisesan accident detection system that detects motor vehicle accidentconditions, where the sensor system comprises an inertial sensor thatsenses motions of the seat and a non-inertial sensor that senses motionsof the seat, and where the control system provides control signals thatcause the actuator to exert a force on the seat in the first degree offreedom, wherein in normal active suspension operation mode the actuatoris controlled to output forces that reduce accelerations of the seat,the method comprising: wherein in the normal active suspension operationmode the control system is responsive to both the inertial andnon-inertial sensors, and in response to the detection of an accidentcondition, the control system becomes responsive only to thenon-inertial sensor, and is not responsive to the inertial sensor.
 22. Amethod for controlling the operation of an active suspension system fora motor vehicle passenger seat, where the active suspension systemcomprises an actuator that is constructed and arranged to place force onthe seat in a first degree of freedom and a control system that isresponsive to a sensor system that detects motor vehicle accelerationsin at least the first degree of freedom and that comprises a system thatdetects one or more of a motor vehicle accident and an imminentaccident, wherein the sensor system comprises at least one sensor thatis part of the active suspension system, where the sensor is constructedand arranged to transmit sensor signals to the control system, and wherethe control system provides control signals that cause the actuator toexert a force on the seat in the first degree of freedom, wherein innormal active suspension operation mode the actuator is controlled tooutput forces that reduce accelerations of the seat, and where the motorvehicle has a vehicle data network that communicatively interconnectsthe active suspension system with a different motor vehicle system, themethod comprising: in response to the detection of an accident or animminent accident, using the control system to operate the actuator toplace force on the seat in the first degree of freedom and communicatingover the network to the different motor vehicle system a signal that isrelated to the accident or imminent accident.
 23. A method forcontrolling the operation of an active suspension system for a motorvehicle passenger seat, where the active suspension system comprises anactuator that is constructed and arranged to place force on the seat ina first degree of freedom, a damper with a variable damping coefficient,where the damper is constructed and arranged to a apply a variableresistive force that opposes relative motion of the seating surface ofthe seat with respect to the seat base, and a spring with a variablespring constant, where the spring is constructed and arranged to placeforce on the seat in the first degree of freedom, and a control systemthat is responsive to a sensor system that detects motor vehicleaccelerations in at least the first degree of freedom, where the sensorsystem comprises an accident detection system that detects motor vehicleaccident conditions, where the control system provides control signalsthat cause the actuator to exert a force on the seat in the first degreeof freedom, wherein in normal active suspension operation mode theactuator is controlled to output forces that reduce acceleration of theseat so as to counteract motions of the seat in the first degree offreedom, the method comprising: detecting, based on the sensor system, arollover of the motor vehicle and in response to the detection of arollover using the control system to provide control signals that causethe actuator to exert a maximum downward force on the seat, cause thespring constant of the spring to quickly decrease, and cause the dampingcoefficient of the damper to be relatively low.
 24. The method of claim23 wherein, in response to the detection of a rollover, after the seatis pulled down by the actuator the control system is used to operate theactuator to output a force that is proportional to the velocity of theseat in the first degree of freedom.